title: Variable delay multi-pulse train for fast chemical exchange saturation transfer and relayed-nuclear overhauser enhancement MRI.
abstract: OBJECTIVE
  Chemical exchange saturation transfer (CEST) imaging is a new MRI technology allowing the detection of low concentration endogenous cellular proteins and metabolites indirectly through their exchangeable protons. A new technique, variable delay multi-pulse CEST (VDMP-CEST), is proposed to eliminate the need for recording full Z-spectra and performing asymmetry analysis to obtain CEST contrast.
  
  
  METHODS
  The VDMP-CEST scheme involves acquiring images with two (or more) delays between radiofrequency saturation pulses in pulsed CEST, producing a series of CEST images sensitive to the speed of saturation transfer. Subtracting two images or fitting a time series produces CEST and relayed-nuclear Overhauser enhancement CEST maps without effects of direct water saturation and, when using low radiofrequency power, minimal magnetization transfer contrast interference.
  
  
  RESULTS
  When applied to several model systems (bovine serum albumin, crosslinked bovine serum albumin, l-glutamic acid) and in vivo on healthy rat brain, VDMP-CEST showed sensitivity to slow to intermediate range magnetization transfer processes (rate < 100-150 Hz), such as amide proton transfer and relayed nuclear Overhauser enhancement-CEST. Images for these contrasts could be acquired in short scan times by using a single radiofrequency frequency.
  
  
  CONCLUSIONS
  VDMP-CEST provides an approach to detect CEST effect by sensitizing saturation experiments to slower exchange processes without interference of direct water saturation and without need to acquire Z-spectra and perform asymmetry analysis.
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA.
authors.forename: Jiadi
authors.initials: J
authors.lastname: Xu
authors.forename: Nirbhay N
authors.initials: NN
authors.lastname: Yadav
authors.forename: Amnon
authors.initials: A
authors.lastname: Bar-Shir
authors.forename: Craig K
authors.initials: CK
authors.lastname: Jones
authors.forename: Kannie W Y
authors.initials: KW
authors.lastname: Chan
authors.forename: Jiangyang
authors.initials: J
authors.lastname: Zhang
authors.forename: P
authors.initials: P
authors.lastname: Walczak
authors.forename: Michael T
authors.initials: MT
authors.lastname: McMahon
authors.forename: Peter C M
authors.initials: PC
authors.lastname: van Zijl
mesh_terms: D000465:Algorithms; D000818:Animals; D001923:Brain Chemistry; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D057054:Molecular Imaging / Q000379:methods*; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014018:Tissue Distribution
keywords: APT; CEST; MTC; VDMP-CEST; chemical exchange; contrast agent; exchange rate; magnetization transfer; pulsed CEST; rNOE-CEST; relayed NOE